Process for the refining of naphthenic acids



Patented May I4, 1946 .ATENT orrics PROCESS FOR THE REF-INING 01 NAPHTHENIU ACIDS Hugh .RogersBen'y, Alton, .111. .assignor to Shell Development Company, San Francisco, cairn,

'a ocrporation of Delaware No Drawing. Application nuym, 19.39, Serial No. 286,238

5 Claims. (01. 260 -514) This invention relates to a method of refining crude naphthenic acid which contains various impurities including acidic organic sulfur compounds and neutral oils. More particularly, my invention relates to th-eimprovement in refining crude naphthenic acid containing normally liquid :organic acidic sulfur compounds, comprising the steps of heating said acids to elevated term peratures to decompose the sulfur compounds Q to neutral oils and gaseous sulfur compounds without effecting substantial decomposition of the naphthenic acids, removing the gases so formed, neutralizing the heat treated naphthenic acids with aqueous caustic alkali and extracting 5 the resulting soapsolution with a solvent for the unsaponifiable impurities.

.Naphthcnic acids are produced largely byexQ tracting unrefined :mineral oils containing the same with alkaline oil-insoluble liquids, and

3 acidifying the extract to liberate extracted naphthenic acids. Naphthenic acids so obtained normally contain large proportions of impurities, chiefly sulfur compounds and neutral oils. These impurities greatly reduce the commercial value 3 and usefulness of the naphthenic acids by reason of lowering their neutralization number and by forming dark, unstable, heavy metal salts,

. such as the lead salts, Presence of these in:-

purities makes the salts unsuitable for use .as

l paint drlers, extreme pressure compounds mineral lubricating oils, adhesives, and for many other purposes.

It is .known that extracting an aqueoussolution of the alkali metal salts of some crude 3 naphthenic acid with a hydrocarbon oillmay remove said impurities. However, I have .found that crude naphthenic acids produced ,fromcertain .mineral oils contain organic sulfur compounds having acidicjproperties so nearly resembling naphthenic acidsin thematterof their acid propertiesthat separation by neutralization with aqueous caustic .alkaliiand extraction with a solvent for the .unsaponifiable impurities is in-.

eficctive in removing said sulfur compounds. 5 Moreover, as these organic acidicsulfur com pounds are normally liquid andmay have boiling ranges comparable .to those of naphthenic acids, separation by distillation isnot feasible.

It iiS a purpose of this invention to provide a" methods of refining crude naphthenic acids by solvent extraction of their aqueous soap solution, so to make this method applicable to naphthenic acids containingyorganic acidic sulfur ccnipoundsnot heretofore separableby simple means. Acids produced in accordance with my 5 invention are capable of forming light-colored} heavy metal salts, and, in particular, lead salts whichdo not "tum black upon preparation or standing.

The acidic sulfur compounds which areso diffi- 1D cult tor-emove from naphthenic acids containing them are believed to be sulfonlc acids or other organic sulfur acids. 1 have found that these acids may be converted to normally gaseous sulfur .compoundsand neutral oils by heating them in a suitable vessel, such as a shell still, at temperatures of about 500 (to 750 F. and preferably at temperatures from 600 to 700 F. without simultaneously decomposing the naphthenic acids lithe time of "heating is properly controlled. This 2 heating may be carried out at substantially atmospheric or superatmospheric pressures. Pressures from 5 tolOO lbs. gauge areespecially con- Venient. "Therefore, I precede the known refining by solvent extraction of the soap solution with 5 a heat treatment for atime sufficient to break down these acidic sulfur compounds. On the other hand, "the time of heating must not be so long, to cause substantial evolution of C02. This canreadily be achieved as naphthenic acids, ingenera'htere sufficiently'stable within the above temperature range to enable substantially complete decomposition of acidicorganic sulfur compounds without decomposition of the naphthenic acids.

The proper time of heating may vary over a considerable range depending upon the exact temperature used. This is obvious from the known fact that the rate of thermal decomposition doubles approximately "with every temporature increment of 22 F. At 685 F. the proper timeis in therrange of Etc 30 minutes, and is more or less,-depending on the temperature, in approximatejaccord with the above law governing the rate of thermal reactions. 5

The gas products formed during the heat treat- A ment areseparated from the naphthenic acid, eithercontinuously or intermittently and may be analyzed irnmediately for CO2. .As soon as the CO2 content "of the waste vapors arises above a certain predetermined maximum the heating is discontinued and the still charge is allowed to cool. The resulting. heat treated naphthenic acids are then neutralized with aqueous caustic After completed treatment as described above,

the clear soap solution is acidified with an aqueous solution of a suitable mineral acid which is stronger than naphthenic acids, such as sulfuric, hydrochloric acid, etc. to liberate the naphthenic acids from the soaps. Liberated naphthenic acids are separated from the resulting aqueous layer and'are washed with water to remove free mineral acid and salts. The washed naphthenic acids may now be used, if desired after distillation for preparing the desired light colored, heavy metal salts, such as lead, cobalt, copper, etc., naphthenates, which are useful for many purposes. Further, if desired, the purified naphthenic acids may be fractionally distilled to produce several grades of the desired naphthenates.

The following example further illustrates our process.

Example A crude naphthenic acid containing about of sulfur acids and other sulfur compounds was placed in a still and heated under lbs. gauge to a temperature of 685 F. The waste gases were vented through a watercooled condenser to condense escaping oil and naphthenic acids. The temperature of 685 F. was maintained for about ten minutes, and as after the lapse of this time the formation of hydrogen sulfide had ceased, the still and its contents were allowed to cool. The recovered liquid distillate was combined with the still bottoms and the mixture neutralized with the stoichiometric quantity of caustic soda. The resulting soap was dissolved in water, heated to about 200 F. to facilitate separation of neutral oils, and the separated neutral oils were removed. The solution was then washed four times with a low sulfur naturally sweet kerosene to remove dark colored neutral oils formed while decomposing the sulfur compounds.

The purified soap solution wasacidified' with dilute sulfuric acid and the separated naphthenic acids recovered. These acids upon distillation yielded Very light colored naththenic acids that upon reacting with litharge formed light colored lead naphthenates. Distilling the original naphthenic acids, without first subjecting them to the purification process, yielded naphthenic acids that upon reacting with litharge formed almost black colored lead naphthenates.

I claim as my invention:

1. In the process of refining crude naphthenic acid containing normally liquid acidic organic sulfur compounds by extracting an aqueous soap solution of said naphthenic acids with a water ganic sulfur compounds thereby converting said 5 organic sulfur compounds to neutral oils and normally gaseous sulfur compounds and to produce heat treated naphthenic acids, separating the said gaseous compounds from the heat treated acids and dissolving said acids in aqueous caustic 1C alkali to form said soap solution.

2. In the process of refining crude naphthenic acid containing normally liquid acidic organic sulfur compounds by extracting an aqueous soap solution of said naphthenic acids with a Water im- 1! miscible solvent for unsaponifiable impurities with which crude naphthenic acids are usually associated, the improvement comprising heating the crude naphthenic acid to a temperature of about 500 F. to 750 F. and under superatmos- 2| pheric pressure for a time sumcient to decompose the organic acidic sulfur compounds to form normally gaseous sulfur compounds and neutral oils and insufiicient to liberate substantial amounts of CO2 and separating the said gaseous 21 compounds from the heat treated acids and dissolving said acids'in aqueous caustic alkali to form said soap solution.

3. In the process of preparing purified naphthenic acid by extracting an aqueous alkaline so- 3 lution of crude naphthenic acids containing normally liquid acidic organic sulfur compounds by extracting an aqueous soap solution of said naphthenic acids with a volatile petroleum distillate,

the improvement comprising heating the crude 3.

naphthenic acid to a temperature of about 600 F. to 700 F. and under a pressure of about 5 to pounds until gaseous sulfur compounds are no longer evolved and separating said sulfur compounds from the heat treated acids and dis- ,5 solving said acids in aqueous caustic alkali to form said soap solution.

4. In the process of preparing purified naphthenic acid by extracting an aqueous alkaline solution of crude naphthenic acids containing 4 normally liquid acidic organic sulfur compounds by extracting an aqueous soap solution of said naphthenic acids with a volatile petroleum distillate, the improvement comprising heating the crude naphthenic acid to a temperature of about 5 600 F. to 700 F. for 5 to 30 minutes and under a pressure of 5 to 100 pounds and separating the gaseous sulfur compounds formed from the heat treated acids and dissolving said acids in aqueous caustic alkali to form said soap" solution. 5

5. In the process of preparingpurified naphthenic acid by extracting an aqueous alkaline solution of crude naphthenic acids containing normally liquid acidic organic sulfur compounds by extracting an aqueous soapsolution of said 6 naphthenic acids with avolatile petroleum distillate, the improvement comprising heating the crude naphthenic acid to a temperature of about 685 F. for about 10 minutes and under a pressure of 35 pounds and separating the gaseous 6 sulfur compounds formed from the heat treated acids and dissolving said acids in aqueous caustic alkali to form said soap solution.

I-IUGl-I ROGERS BERRY, 

